This invention relates to decorating ceramic objects, particularly glass articles such as glass containers. As used herein “glass” should be understood to refer to a wide range of ceramic substrates, including glass. Although decorating glass containers, particularly bottles, is a use for which the invention finds particular utility, it should be understood that the shape of the substrate does not affect the utility of the invention. Decorating may refer to printing discrete words or designs onto the substrate or onto a previously applied coated areas, or it may involve applying a coating (colored or clear, opaque or transparent) onto substantial areas of the substrate. In either case, the process may be referred to as “printing” and the material used may be referred to as “ink.” Application of brand indicia to glass bottles is one commercially important example.
In particular, the present invention deals with the application of two or more layers of organic decoration having different colors in which at least a portion of the layers overlap in direct contact with each other. For example, a colored field may first be applied to the substrate, and then lettering of a different color printed onto the first colored field. When a second decorating layer is printed onto a first decorating layer that has not been sufficiently hardened by curing, there is considerable risk that the first layer will be damaged by the second printing operation. For example, in the screen printing operations typically used in the ceramic decorating industry, contact by the screen in the second printing step often causes uncured portions of the first decorating layer to be lifted from the substrate. A common response to this problem is to cure or at least partially cure a previous decorating layer before applying a second layer, either by passing the articles being decorated through a curing oven or by specialized intermediate curing means such as ultraviolet curing. These additional steps disadvantageously add cost, complexity, and process time to the decorating process. It would be highly desirable if multi-layered organic decorations could be applied to ceramic substrates without the inconvenience and cost of added steps.
In the past, glass decorations have been applied as inorganic frits, which required exposure to high temperatures in order to be fused into a durable film. Ceramic frit decorations, however, suffer from one or more disadvantages, such as the presence of heavy metals, low color brilliance, the necessity of using high temperatures to fuse the frits after application, and often a requirement to subsequently reanneal the labeled bottles. Once ceramic frit decorations are fired onto a glass surface, adhesion is usually excellent, and removal of the decoration is extremely difficult.
Organic decorations have been proposed for decorating bottles to overcome some of these problems, and particularly useful organic decorating compositions are disclosed in commonly assigned U.S. patent application Ser. No. 09/617,847 and in U.S. Pat. No. 6,214,414 B1, the disclosures of which are hereby incorporated by reference. Other organic decorating compositions are disclosed in U.S. Pat. Nos. 3,468,835; 3,471,312; 3,607,349; 5,346,933; and 5,411,768.
It is desirable for coatings applied to bottles to be tough and resistant to marring by abrasion or impact and they should be resistant to degradation by caustic solutions commonly employed for cleaning bottles.
Many earlier bottle decorating compositions were “applied ceramic labels,” that is, they are applied as inorganic frits that are subsequently exposed to high temperatures. Applied ceramic labels, however, suffer from one or more disadvantages, such as the presence of heavy metals, low color brilliance, the necessity of using high temperatures to melt the frits after application, and often a requirement to subsequently reanneal the labeled bottles.
Organic compositions have been used for bottle decorating, but resistance to abrasion and impact strength of many of these coatings were typically low, and resistance to degradation by caustic bottle-cleaning solutions have often also been lower than desired. Organic bottle decorating compositions based primarily on epoxy resins, dicyandiamide curing agent, and siloxane, and usually containing various additional components, are known. See, for example, the following U.S. Pat. Nos. 3,468,835; 3,471,312; 3,607,349; 5,346,933; and 5,411,768.